@Lusephur: That last observation is "normal" eInk ghosting (exacerbated by the way Nickel handles displaying a sleep screen, which is not the worst, but not entirely optimal either).
I don't have a Mk. 6 device myself, and given the sneaky potentially random nature of the results on a Glo HD, I don't really have a better answer than: you're not alone, but it's quite likely a very weird corner-case at a deep hardware level that no-one probably cares about anymore, because it affects an EoL device & platform, and the only people that might have been able to do something about it in the first place are NTX (the OEM that provides the boards for Kobo devices) or even NXP (the people that actually come up with the SoC used on said boards), not even Kobo themselves

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